Microstracture and thermoelectric properties of Na_xCo_2O_4/Ag composite synthesized by the polymerized complex method

摘要

The synthesis of a thermoelectric Na_xCo_2O_4/Ag composite was attempted by the polymerized complex (PC) process using AgNO_3 as an Ag source and subsequent sintering at 115 3 K for 72 ks. The effects of the PC process and Ag addition to Na_xCo_2O_4 on microstructure and thermoelectric properties of the Na_xCo_2O_4/Ag composite were investigated. Ag was hardly substituted for Na and Co sites, and the sintered sample was composed of the Na_xCo_2O_4 and Ag phases. The electrical resistivity of the composite was smaller than that of the Na_xCo_2O_4 single phase and the Seebeck coefficient was slightly enhanced by Ag addition, resulting in the significantly large power factor. However, most of precipitated Ag particles in the Na_xCo_2O_4 matrix were coarse, 5-8 mu m in size, and the thermal conductivity of the composite was high as compared to the Na_xCo_2O_4 single phase. From these results, the dimensionless figure of merit of the composite was almost the same as that of the Na_xCo_2O_4 single phase.